Eastern Baltic cod ( Gadus morhua ) has experienced a dramatic decline in biomass, distribution, size and condition over recent decades, related to a combination of fishing pressure and environmental stressors. Reduced parental size and condition are known to impact reproductive success, affecting egg quality, fertilization and hatching success and larval survival. However, how these reproductive traits vary throughout the spa...

Long‐term ocean warming impacts the marine environment, and these effects will be exacerbated by future climate change affecting, e.g., biogeochemical processes and microbial communities. However, how the sediment microbial cell abundance and live/dead ratio respond to warming is poorly understood. In this study, sediment core samples were collected from a Baltic Sea bay artificially heated on average 5°C for > 50 years above...

Zooplankton are crucial for food webs and biogeochemical cycles. However, warming associated with climate change may alter their seasonal timing and reproductive strategies. This study investigated how long‐term warming impacted zooplankton (mainly copepods) phenology and overwintering strategies by comparing a Baltic Sea bay, heated by warm water discharge for more than 50 yr, with an unaffected control bay. Field observation...

Organisms in systems with seasonality require adaptations that enable them to endure harsh conditions and to emerge again at an optimal time to start a new period of production. One such adaptation is dormant eggs in zooplankton. While there is much information on the cues leading to the production of dormant eggs, less is known about the termination and hatching of these eggs, especially among marine zooplankton. Our results...

Constructed wetlands and constructed floating wetlands are widely used for nitrogen (N) removal from surface water to combat eutrophication in freshwaters. Two main N removal pathways in freshwaters are plant biomass N uptake and denitrification, i.e. transformation of nitrate (NO 3 -) to nitrous oxide (N 2 O) or nitrogen gas (N 2 ) by different microbes possessing nirK , nirS , nosZI, and n osZII genes. In this study, we test...

Thiamin is an essential water‐soluble B vitamin known for its wide range of metabolic functions and antioxidant properties. Over the past decades, reproductive failures induced by thiamin deficiency have been observed in several salmonid species worldwide, but it is unclear why this micronutrient deficiency arises. Few studies have compared thiamin concentrations in systems of salmonid populations with or without documented th...

Top predators in several aquatic food webs regularly display elevated reproductive failure, caused by thiamin (vitamin B 1 ) deficiency. The reasons for these low‐thiamin levels are not understood and information about the transfer of thiamin from the producers (bacteria and phytoplankton) to higher trophic levels is limited. One main concern is whether cyanobacterial blooms could negatively affect thiamin transfer in aquatic...

Copepods are common crustaceans in aquatic systems and one of the most important producers of carotenoid astaxanthin pigments, which can enhance the animals' resistance against potentially damaging ultraviolet radiation (UVR), but at the same time, increases the risk of fish predation. Previous studies have demonstrated that copepods have different pigmentation levels matching the current threat level in terms of UVR and fish...

The purpose of this dataset was to compile adult and offspring size estimates for marine organisms. Adult and offspring size estimates of 408 species were compiled from the literature covering >17 orders of magnitude in body mass and including Cephalopoda (ink fish), Cnidaria (“jelly” fish), Crustaceans, Ctenophora (comb jellies), Elasmobranchii (cartilaginous fish), Mammalia (mammals), Sagittoidea (arrow worms) and Teleost (i...

Most animals, including aquatic crustacean zooplankton, perform strong avoidance movements when exposed to a threat, such as ultraviolet radiation (UVR). We here show that the genera Daphnia and Bosmina instantly adjust their vertical position in the water in accordance with the present UVR threat, i.e., seek refuge in deeper waters, whereas other taxa show less response to the threat. Moreover, Daphnia repeatedly respond to U...

Arctic zooplankton ascend to shallow depths during spring to graze on the yearly occurring phytoplankton bloom. However, in surface waters they are exposed to detrimental ultraviolet radiation (UVR) levels. Here, we quantified concentrations of substances known to have UVR‐protective functions, namely mycosporine‐like amino acids (MAAs) and the carotenoid astaxanthin, from March to May in Calanus finmarchicus , Calanus glacial...

The transparency regulator hypothesis (TRH) proposes that ultraviolet radiation (UVR) is a main driving force behind diel vertical migration (DVM) of zooplankton in clearwater systems. While previous studies have mainly studied DVM in relation to the TRH on a spatial scale across systems we here focus on long‐term trends in a single system in order to assess if UVR explains observed patterns in DVM. We show that the strength o...

Zooplankton accumulate several groups of photoprotective compounds to shield against damaging ultraviolet radiation (UV). One of these groups, the carotenoids, makes the animals more conspicuous to visually hunting predators, whereas others, such as the mycosporine‐like amino acids (MAAs) may not. The blend of photoprotective compounds is therefore important for the UV defense but also for the ability to escape predation throu...

We assessed how zooplankton (copepods) handle the simultaneous threats of predators and ultraviolet (UV) radiation and whether they respond with changes in pigmentation, vertical migration, or both. We found weak vertical migration among copepods in response to UV stress, and this response was not apparently influenced by predation risk. Exposure to high levels of UV radiation caused copepods to retain pigments in the absence...